1. Field of the Invention
The present invention relates to a method for producing an alumina-based porous support used as a catalyst support and the like.
2. Description of the Related Art
An alumina-based porous support as one of industrial catalyst supports employed in various chemical reactions are known.
Such an alumina-based porous support can be produced as follows.
An alumina raw material is extruded into a molded article such as Raschig ring-shaped molded article in a size of several mm and weighing about several hundreds mg.
Such molded article is filled in a saggar. The saggar is filled in a sintering furnace and the molded article is sintered indirectly. After completion of the sintering, an alumina-based porous support thus sintered is removed from the saggar.
In such sintering process, it is essential to perform the sintering at a constant temperature for obtaining an alumina-based porous support having uniform physical properties.
For this purpose, the use of a corner jet burner is proposed in a single furnace.
It is also proposed that the saggar described above is mounted on a cart (See FIG. 4) which travels through a tunnel having a certain temperature gradient (See FIG. 5) whereby effecting the sintering (a tunnel furnace).
In this method, a uniform heating of the inside of the saggar is ensured, for example, by forming the saggar into an appropriate shape. The uniform heating throughout the all sintering containers is ensured by mounting the containers on the carts in an appropriate condition.
However, the conventional methods described above still involve the following problems.
One problem is an insufficient uniformity in the temperature distribution throughout the inside of the furnace because of difficulty in sintering at a high temperature (1500.degree. C. or higher) in a conventional method. Accordingly, it is difficult to obtain an alumina-based porous support having uniform physical properties by means of the conventional method.
Such difficulty in sintering at a high temperature in a conventional method also causes an extremely prolonged sintering period.
Especially, in a furnace having a large capacity, the sintering period is required to be as long as 70 to 80 hours, or sometimes be 1 week to 10 days, approximately.
The absence of the tightly controlled temperature inside of the furnace and the absence of homogeneity in the composition of a raw material (especially in water content) may also contribute to the formation of an alumina-based porous support having a poor catalyst performance. These problems are attempted to be overcome usually by means of adjustment of the furnace temperature and the raw material composition based on the results of investigation of a sintered alumina-based porous support.
Such an adjustment, however, can only be conducted at earliest 80 hours from the beginning of the production when the sintering takes 80 hours. Meanwhile, the molded article is introduced in the furnace and sintered successively during the period before the adjustment. In such a case, a large number of an alumina-based porous support having a low performance or undesirable physical properties are produced successively.
Thus the completion of the sintering within a shorter period is desirable.